S. Cave 
203 
The bursa is very similar to that of the male Ostertagia circumcincta. 
It consists of two membranous wings 170 /x deep, supported on each side 
by externo-dorsal, postero-lateral, medio-lateral, antero-lateral, latero- 
ventral and ventro-ventral ribs ; of these the externo-dorsal and postero¬ 
lateral ribs are straight and narrow, the latter extending to the posterior 
limits of the bursa—while the remainder are curved and pointed at their 
extremities. The median dorsal rib, which is situated between the two 
externo-dorsal ribs, has the marked “ antler ” form as in Ostertagia 
circumcincta, but it differs slightly from the latter in that the lateral 
processes of the branches are situated rather more anteriorly. The 
stem of this rib is 50 p, in length, and each branch 40 p. 
The spicules are 180 p in length (in Ostertagia circumcincta they are 
300 p) and the gubernaculum 100 p. 
The above dimensions are all somewhat greater than those given by 
Ransom ; the following list is a comparison : 
Ostertagia trifurcata. 
Bimensions of 
Cambridge specimen 
Dimensions given 
by Ransom 
Spicule .. .. . 
.. 180m 
180 m 
Gubernaculum 
.. 100m 
90 m 
Distance of cervical papillae from head 
.. 320m 
300 M 
Distance of excretory pore from head 
.. 310 m 
290 m 
Total length 
8‘2 mm. 
7 mm. 
Width : 
head 
18 m 
15 M 
maximum 
.. 110m 
90 M 
Median dorsal rib : 
stem 
.. 50 m 
40-50 M 
branches 
.. 40m 
35-40 M 
Unfortunately it was impossible to take these dimensions from fresh 
specimens, and these discrepancies may therefore be due to the swelling 
effects of the glycerin in which they were mounted—a possibility 
supported by the fact that the chitinous spicules, which are unlikely 
to be affected by this reagent, are identical in length. On the other 
hand these differences in size may be due to the different breed and 
environment of the hosts. 
I have written this note since, as far as I am aware, the occurrence 
of Ostertagia trifurcata has hitherto only been recorded from America. 
14—2 
